Conventionally, a biaxial hinge which couples a first casing provided with a display portion and a second casing provided with a keyboard portion such that these casings can open and close relative to each other via a synchronous rotation mechanism is known from JP Laid-Open Patent Application No. 2016-1052. The synchronous rotation mechanism of the known biaxial hinge comprises a first gear and a second gear respectively attached to a first hinge shaft and a second hinge shaft, an intermediate gear provided between a first gear and a second gear; the synchronous rotation mechanism is structured such that it allows the first casing and the second casing to open and close in a synchronized manner. Since the reduction of the distance between the first hinge shaft and the second hinge shaft has its limits, the reduction of thickness of each of the first casing and the second casing also has its limits. In recent years, the thickness of the notebook PC needs to be reduced, and especially the one using a thin flexible display plate on a display portion requires hinges which are respectively provided with a synchronous rotation mechanism and can couple a first casing and a second casing, wherein both casings are made thin, such that they are openable and closable relative to each other.
One object of the invention is to provide a triaxial hinge which is compatible with a first casing and a second casing, wherein both casings are made thin, as well as can efficiently and quickly open and close both casings in synchronized manner; furthermore, another object of the invention is to provide an electronic device using such a triaxial hinge.